1. Field of the Invention
The present invention relates to an engine starting apparatus. In particular, the present invention relates to an engine starting apparatus in which a starting power transmission is provided between a starter motor and a crankshaft. The starter motor rotates by electric power supplied from a battery. The starting power transmission decelerates the rotation power of the starter motor and transmits the power to the crankshaft.
2. Description of Related Art
Conventionally, such apparatus is already well known by e.g. Japanese Patent No. 3070086. In this apparatus, in a mono-cylinder engine, the starter motor and starting power transmission means are downsized without setting excessively high strength by providing a torque limiter mechanism in a starting power transmission. The torque limiter protects the starter motor against reverse operation of the crankshaft upon engine startup.
Furthermore, as disclosed in e.g. Japanese Published Unexamined Patent Application No. Hei 4-148008, the starter motor and starting power transmission are downsized without setting an excessively high strength. The starter motor is prevented against reverse operation of the crankshaft by opening an exhaust valve through a decompression device in an initial compression stroke upon startup of mono-cylinder engine.
In a mono-cylinder engine, as in the case of the above-described conventional art, the starter motor and starting power transmission can be downsized by providing a torque limiter mechanism or decompression device. However, it is difficult to apply the above conventional art construction to a multi-cylinder engine without any change. Specifically, in a multi-cylinder engine, ignition is made at an early timing in spite of a great amount of inertia of the crankshaft. Accordingly, the crankshaft cannot be started without difficulty unless a limiter weight is set to a large value. Furthermore, the decompression device cannot be actuated within a range of a small crank angle without difficulty, and the downsizing and weight reduction of the starter motor and starting power transmission in the multi-cylinder engine cannot be attained without difficulty.